Recent studies have shown that arachidonic acid can be efficiently converted, in quantity, into 15L-hydroxy-5-,8,11-cis-13-trans-eico-satetraenoic acid by the enzyme lipoxygenase in the presence of a reducing agent. This substance is epoxidized mainly at the 11,12 olefin linkage. It is proposed to use these readily available materials for an efficient and simple chemical conversion to prostanoids. The biological activity of these intermediates and possible peroxyderivatives will be evaluated.